Logged in a few minutes ago after the server came back up. Sharrien (logged in earlier) is still guildless. Ravingronn still shows in guild. So, I suspect the fix tonight might prevent any further deletions, but did not restore lost tags.

When removing a player from a guild, make sure both characters are in the same zone.
Please use the command directly - /guildremove playername
Make sure the player doing the removal has the appropriate guild permissions to do so
Also, note that you must zone or camp to character select for the guild roster to update (after being reinvited)